I have been, for a long time, wondering when to use JFrame and JPanel. I was told by textbook, in-person, and via internet search some reasons, but of course, it took me looking at the Java documentation to figure out that a JPanel has the paintComponent(Graphics); method, which allows you to specify what to do to the object itself, unlike JFrame. Also, JPanels are nestable, allowing for more complex graphics than you could achieve with just one container. I also stumbled upon the fact that a JLabel is also a container. (It even has a freaking layout!) Now my question is: when should I be using a JLabel and when should I be using a JPanel?
//I know that you can put JLabels inside a JPanel, and by accident, that a JPanel is more expensive than a JLabel. I, in the long run, plan on making a cashier game that involves some lightweight container for the "money" that moves to the customer's hand upon clicking. I was thinking about using JLabels for the monetary amounts (dollar bills and coins), and the JPanel to serve as the overhead view of the transaction(s). I was also thinking about invoking repaint() (which, to my understanding, can simulate animation) on the "money labels" themselves. This is a double-question, but would you see this as the least expensive way to go about it?
For the most part, JPanel is a container that allows for better organization. When you need to organize your components of your gui, you should use a JPanel and define a layout for the JPanel. You can also nest JPanels within each other and etc. JLabels don't have the capability of defining layouts for further components to be displayed inside the JLabel.
Here's an example of a app that says "Hello World!!!" without the quotes:
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JLabel;
public class JFrame {
public static void main (strings args[]) {
JFrame frame = new JFrame();
String title = "Hello App";
frame.setTitle(title);
frame.setSize(300, 200);
frame.setDefaultCloseOperation
(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
JPanel panle = new JPanel();
frame.add(panle);
JLabel lable = new JLabel("Hello World!!!");
panle.add(lable);
}
}
The file name is "JFrame.java" without the quotes.
Related
To put it simple, there's a simple java swing app that consists of JFrame with some components in it. One of the components is a JPanel that is meant to be replaced by another JPanel on user action.
So, what's the correct way of doing such a thing? I've tried
panel = new CustomJPanelWithComponentsOnIt();
parentFrameJPanelBelongsTo.pack();
but this won't work. What would you suggest?
Your use case, seems perfect for CardLayout.
In card layout you can add multiple panels in the same place, but then show or hide, one panel at a time.
1) Setting the first Panel:
JFrame frame=new JFrame();
frame.getContentPane().add(new JPanel());
2)Replacing the panel:
frame.getContentPane().removeAll();
frame.getContentPane().add(new JPanel());
Also notice that you must do this in the Event's Thread, to ensure this use the SwingUtilities.invokeLater or the SwingWorker
frame.setContentPane(newContents());
frame.revalidate(); // frame.pack() if you want to resize.
Remember, Java use 'copy reference by value' argument passing. So changing a variable wont change copies of the reference passed to other methods.
Also note JFrame is very confusing in the name of usability. Adding a component or setting a layout (usually) performs the operation on the content pane. Oddly enough, getting the layout really does give you the frame's layout manager.
Hope this piece of code give you an idea of changing jPanels inside a JFrame.
public class PanelTest extends JFrame {
Container contentPane;
public PanelTest() {
super("Changing JPanel inside a JFrame");
contentPane=getContentPane();
}
public void createChangePanel() {
contentPane.removeAll();
JPanel newPanel=new JPanel();
contentPane.add(newPanel);
System.out.println("new panel created");//for debugging purposes
validate();
setVisible(true);
}
}
On the user action:
// you have to do something along the lines of
myJFrame.getContentPane().removeAll()
myJFrame.getContentPane().invalidate()
myJFrame.getContentPane().add(newContentPanel)
myJFrame.getContentPane().revalidate()
Then you can resize your wndow as needed.
Game game = new Game();
getContentPane().removeAll();
setContentPane(game);
getContentPane().revalidate(); //IMPORTANT
getContentPane().repaint(); //IMPORTANT
It all depends on how its going to be used. If you will want to switch back and forth between these two panels then use a CardLayout. If you are only switching from the first to the second once and (and not going back) then I would use telcontars suggestion and just replace it. Though if the JPanel isn't the only thing in your frame I would use
remove(java.awt.Component) instead of removeAll.
If you are somewhere in between these two cases its basically a time-space tradeoff. The CardLayout will save you time but take up more memory by having to keep this whole other panel in memory at all times. But if you just replace the panel when needed and construct it on demand, you don't have to keep that meory around but it takes more time to switch.
Also you can try a JTabbedPane to use tabs instead (its even easier than CardLayout because it handles the showing/hiding automitically)
The other individuals answered the question. I want to suggest you use a JTabbedPane instead of replacing content. As a general rule, it is bad to have visual elements of your application disappear or be replaced by other content. Certainly there are exceptions to every rule, and only you and your user community can decide the best approach.
Problem: My component does not appear after I have added it to the container.
You need to invoke revalidate and repaint after adding a component before it will show up in your container.
Source: http://docs.oracle.com/javase/tutorial/uiswing/layout/problems.html
I was having exactly the same problem!! Increadible!! The solution I found was:
Adding all the components (JPanels) to the container;
Using the setVisible(false) method to all of them;
On user action, setting setVisible(true) to the panel I wanted to
show.
// Hiding all components (JPanels) added to a container (ex: another JPanel)
for (Component component : this.container.getComponents()) {
component.setVisible(false);
}
// Showing only the selected JPanel, the one user wants to see
panel.setVisible(true);
No revalidate(), no validate(), no CardLayout needed.
The layout.replace() answer only exists/works on the GroupLayout Manager.
Other LayoutManagers (CardLayout, BoxLayout etc) do NOT support this feature, but require you to first RemoveLayoutComponent( and then AddLayoutComponent( back again. :-) [Just setting the record straight]
I suggest you to add both panel at frame creation, then change the visible panel by calling setVisible(true/false) on both.
When calling setVisible, the parent will be notified and asked to repaint itself.
class Frame1 extends javax.swing.JFrame {
remove(previouspanel); //or getContentPane().removeAll();
add(newpanel); //or setContentPane(newpanel);
invalidate(); validate(); // or ((JComponent) getContentPane()).revalidate();
repaint(); //DO NOT FORGET REPAINT
}
Sometimes you can do the work without using the revalidation and sometimes without using the repaint.My advise use both.
Just call the method pack() after setting the ContentPane, (java 1.7, maybe older) like this:
JFrame frame = new JFrame();
JPanel panel1 = new JPanel();
JPanel panel2 = new JPanel();
....
frame.setContentPane(panel1);
frame.pack();
...
frame.setContentPane(panel2);
frame.pack();
...
I have a question about using JFrames
(source 1)
import javax.swing.*;
public class FirstSwingExample {
public static void main(String[] args) {
JFrame f = new JFrame();// creating instance of JFrame
JButton b = new JButton("click");// creating instance of JButton
b.setBounds(130, 100, 100, 40);// x axis, y axis, width, height
f.add(b);// adding button in JFrame
f.setSize(400, 500);// 400 width and 500 height
f.setLayout(null);// using no layout managers
f.setVisible(true);// making the frame visible
}
}
(source 2)
import javax.swing.JButton;
import javax.swing.JFrame;
class FrameTest extends JFrame {
public FrameTest() {
JButton b=new JButton("click");//create button
b.setBounds(130,100,100, 40);
add(b);//adding button on frame
setSize(400,500);
setLayout(null);
setVisible(true);
}
}
public class Appl {
public static void main(String[] args) {
new FrameTest();
}
}
My question is:
in source 1 - .add, .setSize, .setLayout and .setVisible are methods of instance of 'f'.
those of methods initialize properties of 'f'.
but in source2 - add, setSize, setLayout and setVisible are methods of a certain super class.
in this source, there are not any JFrame instance. However it just works without problems.
I cannot figure it out. I discovered Container.class and JFrame.class, Frame.class But I couldn't find the part that makes JFrame instance.
in this source, there are not any JFrame instance
This is the incorrect assumption. In the second code base the current instance, the this as it were is a JFrame object. You create the instance when you call new FrameTest(). Since FrameTest inherits from JFrame, all instances will be children of JFrame.
Other unrelated issues:
While null layouts and setBounds() might seem to Swing newbies like the easiest and best way to create complex GUI's, the more Swing GUI'S you create the more serious difficulties you will run into when using them. They won't resize your components when the GUI resizes, they are a royal witch to enhance or maintain, they fail completely when placed in scrollpanes, they look gawd-awful when viewed on all platforms or screen resolutions that are different from the original one.
You'll usually not want to create classes that extend JFrame, since in doing so you are forced to create and display JFrames, when often more flexibility is called for. In fact, I would venture that most of the Swing GUI code that I've created and that I've seen does not extend JFrame, and in fact it is rare that you'll ever want to do this. More commonly your GUI classes will be geared towards creating JPanels, which can then be placed into JFrames or JDialogs, or JTabbedPanes, or swapped via CardLayouts, wherever needed. This will greatly increase the flexibility of your GUI coding.
I have a problem, I set the size for frame, but doesn't work. I found a topic about this, but it's not helpful for me...
I tried with getContentPane().getSize(500,500), but nothing.
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;
public class Mere extends JFrame{
private JPanel b;
public Mere(String titlu){
setSize(500,500);
setLayout(null);
this.getSmth();
pack();
show();
}
public void getSmth(){
JLabel user=new JLabel("User");
user.setBounds(10,10,80,25);
getContentPane().add(user);
JTextField userText=new JTextField(20);
userText.setBounds(100,10,160,25);
getContentPane().add(userText);
JPasswordField pas=new JPasswordField(20);
pas.setBounds(100,40,160,25);
getContentPane().add(pas);
JButton n=new JButton("Register");
n.setBounds(180,80,100,30);
getContentPane().add(n);
JLabel pass=new JLabel("Pass");
pass.setBounds(10,40,100,25);
getContentPane().add(pass);
getContentPane().setVisible(true);
}
public static void main(String[]args){
new Mere("yas");
}
}
You're calling pack(); after calling setSize().
From the Oracle docs
Causes this Window to be sized to fit the preferred size and layouts of its subcomponents. The resulting width and height of the window are automatically enlarged if either of dimensions is less than the minimum size as specified by the previous call to the setMinimumSize method.
So you rather override the getPreferredSize() method or remove the pack() call. See Should I avoid the use of setPreferred/Maximum/MinimumSize? (YES)
However the best practice would be to use a layout manager (as explanined below) and then call pack() and let the manager do it's job while calculating the preferredSize for you
Also you're using a null layout. Swing was designed to work with different PLAFs and screen sizes and resolutions, while pixel perfect GUIs might seem like the best and faster approach to make a complex GUI the more you advance in this the more problems you'll have in maintain it due to this, so go ahead and use a proper Layout Manager or combinations of them. See Null Layout is Evil and Why is it frowned upon to use a null layout in Java Swing?
Another thing is that you're not placing your program on the Event Dispatch Thread (EDT), see SwingUtilities.invokeLater() why is it needed? and this answer for an example on how to use it
Another thing I see is that you're extening JFrame which translated to english it says that your class is a JFrame, JFrame isn't flexible when you need to add it to another Component, instead you should create a JFrame instance and if you really need to extend something, extend from a JPanel.
To put it simple, there's a simple java swing app that consists of JFrame with some components in it. One of the components is a JPanel that is meant to be replaced by another JPanel on user action.
So, what's the correct way of doing such a thing? I've tried
panel = new CustomJPanelWithComponentsOnIt();
parentFrameJPanelBelongsTo.pack();
but this won't work. What would you suggest?
Your use case, seems perfect for CardLayout.
In card layout you can add multiple panels in the same place, but then show or hide, one panel at a time.
1) Setting the first Panel:
JFrame frame=new JFrame();
frame.getContentPane().add(new JPanel());
2)Replacing the panel:
frame.getContentPane().removeAll();
frame.getContentPane().add(new JPanel());
Also notice that you must do this in the Event's Thread, to ensure this use the SwingUtilities.invokeLater or the SwingWorker
frame.setContentPane(newContents());
frame.revalidate(); // frame.pack() if you want to resize.
Remember, Java use 'copy reference by value' argument passing. So changing a variable wont change copies of the reference passed to other methods.
Also note JFrame is very confusing in the name of usability. Adding a component or setting a layout (usually) performs the operation on the content pane. Oddly enough, getting the layout really does give you the frame's layout manager.
Hope this piece of code give you an idea of changing jPanels inside a JFrame.
public class PanelTest extends JFrame {
Container contentPane;
public PanelTest() {
super("Changing JPanel inside a JFrame");
contentPane=getContentPane();
}
public void createChangePanel() {
contentPane.removeAll();
JPanel newPanel=new JPanel();
contentPane.add(newPanel);
System.out.println("new panel created");//for debugging purposes
validate();
setVisible(true);
}
}
On the user action:
// you have to do something along the lines of
myJFrame.getContentPane().removeAll()
myJFrame.getContentPane().invalidate()
myJFrame.getContentPane().add(newContentPanel)
myJFrame.getContentPane().revalidate()
Then you can resize your wndow as needed.
Game game = new Game();
getContentPane().removeAll();
setContentPane(game);
getContentPane().revalidate(); //IMPORTANT
getContentPane().repaint(); //IMPORTANT
It all depends on how its going to be used. If you will want to switch back and forth between these two panels then use a CardLayout. If you are only switching from the first to the second once and (and not going back) then I would use telcontars suggestion and just replace it. Though if the JPanel isn't the only thing in your frame I would use
remove(java.awt.Component) instead of removeAll.
If you are somewhere in between these two cases its basically a time-space tradeoff. The CardLayout will save you time but take up more memory by having to keep this whole other panel in memory at all times. But if you just replace the panel when needed and construct it on demand, you don't have to keep that meory around but it takes more time to switch.
Also you can try a JTabbedPane to use tabs instead (its even easier than CardLayout because it handles the showing/hiding automitically)
The other individuals answered the question. I want to suggest you use a JTabbedPane instead of replacing content. As a general rule, it is bad to have visual elements of your application disappear or be replaced by other content. Certainly there are exceptions to every rule, and only you and your user community can decide the best approach.
Problem: My component does not appear after I have added it to the container.
You need to invoke revalidate and repaint after adding a component before it will show up in your container.
Source: http://docs.oracle.com/javase/tutorial/uiswing/layout/problems.html
I was having exactly the same problem!! Increadible!! The solution I found was:
Adding all the components (JPanels) to the container;
Using the setVisible(false) method to all of them;
On user action, setting setVisible(true) to the panel I wanted to
show.
// Hiding all components (JPanels) added to a container (ex: another JPanel)
for (Component component : this.container.getComponents()) {
component.setVisible(false);
}
// Showing only the selected JPanel, the one user wants to see
panel.setVisible(true);
No revalidate(), no validate(), no CardLayout needed.
The layout.replace() answer only exists/works on the GroupLayout Manager.
Other LayoutManagers (CardLayout, BoxLayout etc) do NOT support this feature, but require you to first RemoveLayoutComponent( and then AddLayoutComponent( back again. :-) [Just setting the record straight]
I suggest you to add both panel at frame creation, then change the visible panel by calling setVisible(true/false) on both.
When calling setVisible, the parent will be notified and asked to repaint itself.
class Frame1 extends javax.swing.JFrame {
remove(previouspanel); //or getContentPane().removeAll();
add(newpanel); //or setContentPane(newpanel);
invalidate(); validate(); // or ((JComponent) getContentPane()).revalidate();
repaint(); //DO NOT FORGET REPAINT
}
Sometimes you can do the work without using the revalidation and sometimes without using the repaint.My advise use both.
Just call the method pack() after setting the ContentPane, (java 1.7, maybe older) like this:
JFrame frame = new JFrame();
JPanel panel1 = new JPanel();
JPanel panel2 = new JPanel();
....
frame.setContentPane(panel1);
frame.pack();
...
frame.setContentPane(panel2);
frame.pack();
...
I'm very new to Java but have some experience with C++. This is a homework assignment so I'm really just looking for someone to point me in the right direction.
The assignment requires a JFrame with JPanel objects displaying every card in a deck in a 13x4 grid. The Professor has supplied us with some code to get us started:
import javax.swing.*;
import java.awt.*;
public class Main
public static void main(String[] args)
{
//load the card image from the gif file.
final ImageIcon cardIcon = new ImageIcon("cardImages/tenClubs.gif");
//create a panel displaying the card image
JPanel panel = new JPanel()
{
//paintComponent is called automatically by the JRE whenever
//the panel needs to be drawn or redrawn
public void paintComponent(Graphics g) {
super.paintComponent(g);
cardIcon.paintIcon(this, g, 20, 20);
}
};
//create & make visible a JFrame to contain the panel
JFrame window = new JFrame("Title goes here");
window.add(panel);
window.setPreferredSize(new Dimension(200,200));
window.pack();
window.setVisible(true);
}
}
I have tried out a few things, but I can't seem to get multiple panels to display. Should I use a gridLayout() feature? or just create multiple panels and specify each one's location in the frame?
Again if someone can just point me in the right direction that would be awesome.
For displaying elements at the same size, evenly distributed within the container, then yes, GridLayout would be a good choice.
If you need to display the components in the grid at there preferred size (which may be different for each component) then GridBagLayout would be a better choice
If the code was supplied by a your professor, then you need to go back and make them fix it.
Firstly, a JLabel would be easier and provide better support for what you are trying to achieve...
Secondly, because the JPanel doesn't override getPreferredSize, most of the layout managers will set the size of the component to 0x0
There is a way to display multiple JPanels in one JFrame. Unlucky you the way is not so easy. Java has many diffrent LayoutManagers.
For your purpose I would recommend GridBagLayout, it is more complex, but definately the thing you need.
Here is a good tutorial, which helped me to understand it:
GridBagLayout
Hope it is a help.